a) Field of the Invention
The invention is directed to a process for arranging an angle graduation or angle scale at an index disk for rotational measurement systems, wherein the index disk is provided with a central opening for mounting on a carrier shaft, and further to an index disk which is produced in particular according to a process of the type mentioned above for rotational measurement systems with an angle scale arranged thereon and with a central opening for mounting on a carrier shaft.
b) Description of the Related Art
Index disks are used as scale carriers or code carriers in rotational measurement systems for measuring the rotational position of two objects moving relative to one another, e.g., for measuring angles, rotational paths or the like. For this purpose, the angle scale which is arranged on the index disk and which rotates relative to a sensing unit is sensed by the latter and the obtained sensed information is then converted by means of an evaluating unit into corresponding information, e.g., pertaining to the angle of rotation or the like. The sensing is carried out by means of suitable sensing methods, wherein photoelectric, magnetic, inductive or capacitive sensing are used in particular. Common to all of these methods, however, is the fundamental principle that the angle scale, which is generally periodic (incremental), must be centered relative to the axis of rotation of the index disk, so that the sensing information represents a measurement of the relative rotational position of the two objects moving relative to one another. In absolute angle measurement systems or in rotation sensors, information about the absolute rotational angle is generally obtained from the rotational angle information of a plurality of angle scales which are arranged concentrically on the index disk.
The achievable rotational angle measuring accuracy is decisively determined by, among others, the accuracy of the angle scale and by the deviations occurring as a result of the eccentricity of the scale relative to the support, i.e., relative to the axis of rotation of the receiving carrier shaft.
The angle scales to be arranged on the index disks can be produced economically with very high accuracy, especially for sensing based on photoelectric principles. For example, standard incremental disks with an angle indexing accuracy of less than 2 angle seconds are already available.
However, a much greater and more complex problem is that of the eccentricity of the scale relative to the support or axis of rotation of the carrier shaft. Depending on the angle measurement accuracy and angular resolution to be achieved, the use of index disks of different constructions formed of various materials is taken into consideration primarily from a cost stand point.
In this connection, very thin electroformed and photo-etched index disks are known which, while having relatively good centricity of the angle scale relative to the receiving bore, have strict limitations with respect to the angular resolution that can be achieved and are very sensitive as regards handling.
High angular resolutions and high angular resolution accuracies can be realized advantageously with glass index disks. However, these glass index disks have the disadvantage that the receiving bore can be produced at reasonable cost only with very rough tolerances, so that they cannot be used in the assembly process for centering on the carrier shaft. Therefore, specifically for purposes of centering, index disks of this kind are provided with a centering circle for adjusting the position of the index disk on the carrier shaft. This commonly used adjustment process requires special auxiliary sighting means for viewing the adjustment circle, e.g., adjusting microscopes or video cameras, and is also very time-consuming.